The present disclosure relates to an engine starter.
There exists an engine starter that is constructed as shown in FIGS. 1, 2, 3A, and 3B. A motor (electric motor) M of an engine starter 1 uses a general-purpose brush-type DC motor. A base end of a motor shaft 2 is axially and rotatably supported on an end cover 3a that closes a base end side opening of a cylindrical yoke 3. A commutator 4 is integrally fitted onto a tip end of the motor shaft 2. To an outer periphery of the commutator 4, in a tip end side opening of the yoke 3, a ring-shaped holder stay 5 is mounted.
Reference numeral 6 denotes a bottomed cylindrical case (see FIG. 1). The case 6 forms a reduction gear D that is disposed to a tip end side of the motor M, that is, adjacent to the holder stay 5. In the case 6, a tip end 2a of the motor shaft 2 is installed. A base end of a drive shaft 7 is also disposed in the case 6 so as to rotatably fit onto the motor shaft tip end 2a. In the case 6, a plurality of planet gears 8 are also concentrically disposed with respect to the motor shaft tip end 2a so as to engage with the motor shaft tip end 2a and rotate circumferentially inside the case 6 according to the rotation of the motor shaft 2. A ring-shaped support plate 9 is also installed in the case 6 so as to be integrated with the planet gears 8 via a support shaft 9a. By fitting an inner peripheral surface of the support plate 9 integrally onto the drive shaft 7, a circumferential rotation of the planet gears 8 is interlocked with and joined to the drive shaft 7. A driving force of the motor M is thus transmitted to the drive shaft (pinion shaft) 7 in a reduced speed manner.
A unidirectional rotation clutch system C is disposed on a tip end of the drive shaft 7 (see FIG. 1). A clutch outer 10 of the clutch system C is formed of a stepped cylinder. The clutch outer 10 is fit onto the drive shaft 7 such that a helical spline 10a that is formed on an inner peripheral surface of a small-diameter cylinder is engaged with a helical spline 7a that is engraved in an outer peripheral surface of the tip end of the drive shaft 7. When relative rotation occurs between the drive shaft 7 and the clutch outer 10 in a predetermined rotating direction from a side of the drive shaft 7, the clutch outer 10 rotatively moves along the helical spline 7a of the drive shaft 7 and then moves to an active position on a tip end side (a position shown in a lower half of FIG. 1) from an inactive position (a position shown in an upper half of FIG. 1) on the base end side of the drive shaft 7. To an inside of a large-diameter cylinder on a tip end side of the clutch outer 10, a clutch inner 12 is joined that includes a pinion gear 11 that is formed on a tip end outer periphery and engages with a ring gear 11 a on an engine side. The clutch inner 12 moves axially and integrally with the clutch outer 10.
Reference numeral 13 denotes a clutch roller to be interposed between the clutch outer 10 and the clutch inner 12 (see FIGS. 1, 2, 3A, and 3B). Reference numeral 14 denotes a spring that urges the clutch roller 13 toward a side of a clutch outer wall. The clutch roller 13 is housed in a roller chamber 10g that is recessed in an inner peripheral surface of the clutch outer 10. In the roller chamber 10g, as shown in FIG. 2 and FIGS. 3A and 3B, an opposing distance is larger between the clutch inner 12 and the clutch outer 10 at a rotation side end 10b of a clockwise side so as to allow the clutch roller 13 to freely rotate. The opposing distance is narrower toward an engagement side end 10c of a counterclockwise side. When the motor M is halted, as shown in FIG. 2 and FIG. 3A, the clutch roller 13 is positioned at an intermediate position between ends 10b and 10c because of an urging force of the spring 14. In this state, because the clutch roller 13 does not engage with the clutch outer 10 and the clutch inner 12, a driving force is not transmitted. When the clutch outer 10 rotates clockwise, as shown by an arrow in FIG. 2, in response to driving of the motor M, then the clutch roller 13 moves to an engagement side end 10c, which is shown in FIG. 3B. An engaged state is thus set; and a rotating force of the clutch outer 10 is transmitted to the clutch inner 12 via the clutch roller 13. As a result, an engine starts.
When the engine starts, an overrun occurs such that rotation of the clutch inner 12 is faster than that of the clutch outer 10. As shown in FIG. 3A, the clutch inner 12 then rotates counterclockwise (an arrow direction) relatively to the clutch outer 10. The clutch roller 13 then moves toward the rotation side end 10b and freely rotates. This clutch unit thus functions as a one-way clutch unit that prevents the engine driving force from being transmitted to a side of the clutch outer 10 from the clutch inner 12 (see Japanese Published Examined Utility Model Application No. S59-26107 and Japanese Published Unexamined Utility Model Application No. H05-42675, for example).